Method for production of titanium dioxide granules



United States Patent 01 hce 3,403,977 Patented Oct. 1, 1968 3,403,977METHOD FOR PRODUCTION OF TITANIUM DIOXIDE GRANULES Kenneth W. Heywood,Overland, and Charles R. Trampier, Jr., Webster Groves, Mo., assignorsto National Il'lcad Company, New York, N.Y., a corporation of New erseyNo Drawing. Filed June 25, 1964, Ser. No. 378,044 3 Claims. (Cl. 23202)ABSTRACT OF THE DISCLOSURE This invention covers the preparation of anonpigmentary titanium dioxide granular material having a Tyler screensize range from -10 mesh to +400 mesh, with at least 75% +325 mesh, thegranular material made up of individual particles of Ti having a sizefrom 0.07 to 0.1 micron. Such a material is free-flowing and is capableof being handled without dusting.

Such a material is prepared by the process of the instant inventionwhich comprises hydrolyzing a titanium sulfate solution at relativelylow titanium concentration and at relatively low temperatures, calciningthe hydrate and subdividing the calcined product to form Ti0 granules ofthe type described above.

This invention relates in general to the production of titanium dioxide.More specifically it relates to an improved type of nonpigmentarytitanium dioxide in the form of granules useful in the glass industry.

Titanium dioxide is most commonly known and widely used as a pigment forpaints, and as such is generally produced commercially by the socalledsulfate process in which a titaniferous material is digested at elevatedtemperatures with concentrated sulfuric acid to form a porous cake whichis dissolved in water or weak acid, with agitation, to form a solutionof titanium and iron sulfates. The ferric sulfate values in the solutionare converted to ferrous sulfate by the addition of scrap iron. Thesolution is then clarified to remove, by settling and filtration,essentially all of the solid materials contained in the solution withminimum loss of TiO Following clarification the ferrous iron values inthe solution are crystallized to form copperas which is removed from thesolution by filtration. The filtrate is then concentrated to removeexcess water, both steps being necessary to prepare the solution forhydrolysis.

Concentration, as practiced in the prior art, is continued until thespecific gravity of the solution is at least 1.6 with a TiO content ofat least 220 grams per liter and preferably from 225-275 grams perliter. The concentrated titanium sulfate solution is then converted, byhydrolysis, from the soluble state into insoluble titanium hydrate. Thusa predetermined amount of concentrated solution having a TiO content ofat least 220 grams per liter is preheated to a temperature of at least90 C. and added at a predetermined rate, with agitation, to water atsubstantially the same temperature and in the ratio of 3-19 partssolution to one part water. During subsequent boiling, the precipitatedinsoluble TiO forms initially as colloidal particles, which subsequentlyfiocculate to produce a filterable TiO hydrate containing from 30% to36% solids.

In order to meet the high standards set for commercial grades ofpigment, usually nuclei are employed which may be formed in situ duringhydrolysis or produced separately and added to the titanium sulfatesolution prior to hydrolysis. Following precipitation the hydrate isfiltered, washed and bleached to remove impurities, and then givenprecalcination treatments, calcined and finished according to techniqueswell known in the art.

The finished titanium dioxide pigment of the prior art, sometimesreferred to hereinafter as pigmentary TiO will have a particle sizerange of from 0.1 to 1.0 micron with most of the particles being from0.15 to 0.35 and as such is especially useful in paint formulations.

It has been found however that when a pigmentary TiO is added to a batchof molten glass, for purposes of opacifying the glass or otherwiseenhancing its properties or appearance, the pigmentary TiO because ofits inherent stickiness and relatively fine particle size, tends to formlarge fiocs in the molten glass batch which do not melt properly. Infact in most cases substantially all of the titanium dioxide added tothe glass batch sinks to the bottom of the vessel and remains as asintered and unreacted sludge in the glass melt.

Attempts have been made to overcome this tendency of pigmentary TiO tofloc in a glass melt by using a coarser grade of titanium dioxide; andwhile some of the coarser grades have been used successfully in ceramicfrits, these coarser grades of TiO have been found to dust so severely,when introduced into a molten glass batch, as to be uneconomical in theglass industry.

An object of the instant invention therefore is to produce anonpigmentary, free-flowing titanium dioxide material which can be addedto a molten glass batch without dusting and without settling to thebottom of the glass batch. A further object is to produce titaniumdioxide granules which melt rapidly in and disperse uniformly throughouta molten glass bat-ch. These and other objects will become more apparentfrom the following more complete description of the instant invention.

Broadly, this invention contemplates a nonpigmentary titanium dioxidegranular material capable of melting rapidly in a molten glass batchwithout dusting or settling, said granular material having a Tylerscreen size range from l0 mesh to +400 mesh, with at least +325 mesh,said granular material consisting essentially of aggregated titaniumdioxide particles, said particles having an individual size range fromabout 0.05 to 0.15 micron most of which are from 0.07 to 0.1 micron,said material having a bulk density which falls within the range of 0.8to 1.7 grams per cubic centimeter, said material being free-fiowing andcapable of being handled without dusting.

This invention further contemplates producing said nonpigmentarytitanium dioxide granular material by calcining, at a temperature from800 C. to 1000 C., a titanium hydrate produced by hydrolyzing a titaniumsulfate solution of relatively low titanium concentration at relativelylow temperatures, to form, upon calcination, nodules of aggregatedtitanium dioxide particles; and subdividing said nodules into granuleshaving a particle size which falls within the range of 10 mesh to +400mesh, with at least 75% +325 mesh, said granules being freeflowing.These granules comprise aggregated particles of TiO the individualparticles of Ti0 having a size which falls within the range of 0.05 to0.15 micron.

It has been discovered that TiO granules having these characteristicscan be incorporated into a molten glass batch composition withoutdusting and without sludging; and further, that the H0 granules meltrapidly and disperse thoroughly throughout said molten glasscomposition.

This invention further contemplates a novel process for producing thesefree-flowing, nondusting, nonpigmentary titanium dioxide granules whichcomprises the following steps:

(1) Digesting a titaniferous material in concentrated sulfuric acid toform a digestion cake,

(2) Dissolving said cake in aqueous media,

(3) Reducing the iron values to the ferrous state,

(4) Clarifying said solution to obtain a titanium sulfateiron sulfatesolution having a concentration falling within the range of 100-180g.p.l. titanium, calculated (5) Heating water for hydrolysis to at least80 C., the volume of said water substantially equal to to 100% of theamount of solution to be used.

(6) Adding the titanium solution at a temperature from 4080 C. to theheated water with agitation over a period of 50 minutes and maintainingthe temperature of the hydrolysis mixture from 6080 C. during theaddition period,

(7) Heating the hydrolysis mixture to boil over a period of from 15 to75 minutes,

(8) Boiling for about 1-3 hours to form a rapid settling titaniumhydrate,

(9) Filterinig, washing, bleaching and then calcining at 800l000 C. toform nodules of aggregated titanium dioxide particles, and

(10) subdividing said nodules to form granules which pass through a 10mesh screen and are retained on a 400 mesh screen, with at least 75%being +325 mesh. In carrying out the instant invention, substantiallyany type of titaniferous material may be used. The ore or concentrateemployed is digested with concentrated sulfuric acid in the mannercurrently employed in the industry. The titaniferous material is heatedat elevated temperatures in the presence of concentrated sulfuric acidto digest the titaniferous material and form therefrom a porousdigestion cake containing titanium and iron sulfates. After curing, thecake is dissolved in an aqueous media such as water or weak acid to forma solution of iron and titanium sulfates.

As the digestion cake is dissolved, scrap iron is added to the solutionto reduce the ferric iron values to ferrous sulfate. The solution isthen clarified in the usual manner to remove slimes and insolublematerial. In accordance with the novel features of this invention theclarified solution should have titanium concentration of from 100 to 180g.p.l. calculated as TiO and an H SO /Tio ration from 1.7 to 2.3.

At this stage, i.e., without crystallization or further concentrationthe clarified solution is ready for hydrolysis. It should be noted thatthe concentration of the titanium values is realtively low, i.e., from100 to 180 g.p.l. titanium as TiO which is far below the titaniumconcentration used today in the commercial production of pigments whichis at least 220 g.p.l. TiO Moreover, since the hydrolysis step iscarried out with solutions at these low concentrations, crystallizationof the iron values is not required. The process of the instant inventiontherefore eliminates both the crystallization step and the subsequentconcentration step required in normal TiO pigment production methods.

The solution containing from 100 to 180 g.p.l. titanium, calculated asTiO and having an H SO /TiO ratio between 1.7 and 2.3 is then hydrolyzedunder novel controlled conditions to produce a titanium hydrate suitablefor the production of the nonpigmentary TiO of this invention. This maybe accomplished by a variety of methods, three of which are describedbriefly as follows:

(1) The solution is heated to 4080 C. and added with agitation to waterin the amount from 10% to 100% of the amount of solution used, the waterbeing heated to at least 80 C. over a period of from 15 to 50 minutes,the temperature of the hydrolysis mixture being allow to drop to 60 C.to 80 C. or maintained within this temperature range during the additionperiod. The mixture is then heated to boil and boiled for 13 hours. (2)The solution is heated to 4080 C. and a separately prepared nuclei isadded to the solution and the solu tion is heated to boil over a periodof 15-75 minutes and boiled for 13 hours.

(3) The procedure described in (1) above is utilized except that only toof the titanium sulfate solution is added to the water during theaddition period, the remaining 10% to 25% of the solution being addedafter the hydrolysis mixture has been brought to boiling temperature andboiled for from 10 minutes to minutes. After the remaining solution hasbeen added, the entire mixture is then boiled for from 1 hour to 3 hoursto complete the hydrolysis.

Certain advantages may be realized when process (3) is employed sincethe hydrate formed tends to settle faster and filter more rapidly thanthe hydrate produced by the other two methods (1) and (2). Theseadvantages may be of particular value when it is desired to handle largequantities of hydrate.

The titanium hydrate obtained by any of these processes is filtered,washed, bleached. The titanium hydrate so obtained is then calcined at800l000 C. to form nodules of aggregated TiO The nodules are then brokenup into granules which pass a 10 mesh screen but are retained on a 400mesh screen with at least 75% being +325 mesh.

The granular titanium dioxide material produced is subjected to varioustests in order to determine some of its physical properties. These testsare described as follows:

DUSTING TEST 100 grams of the granular material were placed in a 24 inchglass tube having an ID. of 3/ inch and having a 7.5 cm. Buchner funnelat one end to act as an air dispenser. The tube should be held at 30angle to keep the granular material out of the Buchner funnel as it isbeing added to the tube. Air at the rate of 10:0.02 cu. ft./min. ispassed through the tube while held in a vertical position for 5 minutesafter which the granular material is collected and weighed. The weightloss calculated in percentage is recorded as the loss due to dusting. Ithas been found that the granular material of the instant invention has adust loss of less than 7%.

FREE-FLOWNG TEST The titanium dioxide granular material is placed in aglass funnel and the material is allowed to pour through the funnelwithin a certain time period if it is considered to be free-flowing. Inthis particular test a glass funnel having a discharge opening of /8inch, a top opening of 4% inches, a 3 inch cone height, a 60 cone, and 1inch stem was used. Sufficient granular material was added to fill thecone (about grams). The opening of the funnel was closed as the funnelwas filled. Upon opening the discharge end of the funnel, the time wasmeasured for the funnel to become emptied. The interval of time isrecorded as the amount of free flow that the granular materialpossessed. In most cases the material flowed through the funnel withinless than 6 seconds.

BULK DENSITY A 10 mesh scren is placed on top of a 8 inch diameter, 60cone funnel having a inch discharge opening. A 50 ml. cup was placed atthe tip of the funnel discharge opening. The TiO sample was then brushedthrough the screen which passed through the funnel and into the cup. Thecup was filled to overflowing, leveled off with a spatula and thecontents of the cup weighed.

In order to further describe the instant invention, the followingexamples are presented:

EXAMPLE I A titanium sulfate-ferrous sulfate solution was prepared inthe usual manner by reacting an ilmenite ore ground to 200 mesh withconcentrated sulfuric acid to produce a digestion cake which wasdissolved in weak sulfuric acid, scrap iron was added to the solution toreduce the ferric iron values to ferrous iron. The solution was thenclarified to remove slimes and insoluble materials. The clarifiedsolution had the following analysis:

The titanium values in solution were then hydrolyzed at the aboveconcentration without crystallizing any of the ferrous sulfate valuesfrom the solution. To this end 1250 parts of water were placed in aprecipitation tank and were heated to 95 C. 2500 parts of the titaniumsulfateferrous sulfate solution previously heated to 55 C. were added tothe hot water under agitation over a period of 30 minutes. Thetemperature of the hydrolysis was allowed to fall to about 70 C. andmaintain at 70 C. during the addition period. The temperature of themixture was then increased to a boil within 30 minutes and the mixturewas boiled for 3 hours to hydrolyze the titanium values. The batch wasthen diluted with 5600 parts of hot water and the hydrolyzed titaniumvalues were recovered as a hydrate by filtration and thorough washing. Arecovery of 95% of the titanium values was obtained. The washed hydratewas bleached, washed, dewatered and calcined to a temperature of 875 C.in a rotary furnace. No dusting occurred in the calciner during thecalcining operation. The calcined product consisted of nodules /2 toinch in diameter. These nodules were passed rapidly through a hammermill (with no screen) to subdivide these nodules into granules of a sizesuch that they passed through a mesh screen but were retained on a 400:mesh screen with 91% +325 mesh.

These granules had the following Tyler screen analysis: Percent -10 meshmesh 6.1 20 mesh +40 mesh 18.8 -40 mesh +60 mesh 16.9 60 mesh +80 mesh15.8 80 mesh +100 mesh 7.7 -100 mesh +325 mesh 25.7 325 mesh +400 mesh9.0

The size of the individual particles in the granules were 0.05 micron to0.15 micron with most of the particles being from 0.07 to 0.1 micron asdetermined by an electron photomicrograph. The bulk density of thegranular material was 1.4 grams per cubic centimeter. The dust loss was2.3% and the material had a free flow of 5 seconds. It should also benoted that the nodules were hard enough to withstand micropulverizing(without a screen) 'without producing 400 mesh material.

EXAMPLE I-A In order to show the effectiveness of the instant inventionin a molten glass batch; 4.0 parts of the titanium dioxide granules wereadmixed by dry blending with a plate glass composition comprising 68.7parts of SiO 0.5 part of A1 0 23.1 parts of CaCO 13.7 parts of NaNO 14.0parts of Na CO and 1.0 part of As O This plate glass composition,containing the free-flowing, nondusting TiO granules, was melted at1500C. and held at 1500 C. for 1 hour. All of the ingredients meltedrapidly and a homogeneous glass mixture was obtained. None of the T iOadded was lost through dusting or sludging.

EXAMPLE IB Another type of glass was prepared using the TiO granules ofthe instant invention. This particular glass composition had thefollowing ingredients: 56 parts SiO' A1 0 31.4 parts of MgCO and 9 partsof Ti0 granules. The molten glass batch was prepared in the same manneras that described in Example I-A above and again excellent results wereobtained. The TiO granules melted rapidly in the molten glass batch andno dusting or sludging occurred.

Example I-C For comparative purposes regular pigment grade Ti0 was usedin the glass composition of Example =I-A instead of the TiO granules ofthe instant invention. The regular pigment grade TiO formed largeagglomerates in the glass batch and settled to the bottom of the glasssmelter. Only 30% of the TiO added dissolved; the remaining 70% formedan insoluble sludge in the bottom of the smelter and was lost from theglass batch.

Example II This example illustrates a modification of the method ofhydrolyzing the titanium sulfate-ferrous sulfate solution as disclosedin Example I, in which a separately prepared nucleus was used.

The nucleus employed was prepared as follows: 200 parts of water wereheated to 100 C. and to the water were added 600 parts of titaniumsulfate-ferrous sulfate solution heated to 50 C. over a period of 13-17minutes with agitation and held at 75 C. to produce a collodialsolution.

1200 parts of the titanium sulfate-ferrous sulfate solution described inExample I and containing 132 grams of Ti0 per liter were heated to 55 C.and to this solution were added with agitation 800 parts of theexternally prepared nuclei. The mixture was headed to boiling over aperiod of 60 minutes and boiled for 3 hours to hydrolyze the titaniumvalues. The titanium hydrate produced was washed, bleached, dewateredand calcined in the manner described in Example I. The calcined nodulesproduced had substantially the same physical characteristics as thosedescribed above. These nodules were then passed through a hammer millwithout a screen and the granules produced were similar to thoseobtained in Example I. Again the granules had a screen size within therange of 10 mesh +400 mesh with at least 75% +325 mesh. The size of theindividual particles in the granules was 0.05 to 0.15 micron. The bulkdensity of the granules was 1.1 grams per cubic centimeter. Thefree-flow was 5 seconds and the dust loss was 4.5%. These granules werealso added to molten glass batches, such as described in Examples I-Aand I-B, and again no dusting nor sludging of the Ti0 granules occurred.

Example III In this example the procedure of method (3) was employed inwhich of the titanium solution was added at the outset and the remaining15% was added after the hydrolysis mixture had boiled for 60 minutes.

Again the titanium sulfate-ferrous sulfate clarified solution describedin Example I was used in this example.

1250 parts of water were placed in a precipitation tank and'were heatedto C. 2125 parts of the titanium sulfate-ferrous sulfate solutionpreviously heated to 55 C. were added to the hot water under agitationover a period of 26 minutes. This amount was 85 of the total amount ofsolution to be added. The temperature of the hydrolysis was allowed to'fall to about 70 C. and maintained at 70 C. during the addition period.The temperature of the mixture was then increased to a boil Within 35minutes and the mixture was boiled for 1 hour to hydrolyze the titaniumvalues. 375 parts of the remaining titanium solution were then added tothe boiling mixture over a period of 5 minutes and then the wholemixture was boiled for an additional 2 hours to complete the hydrolysis.The batch was then diluted with 5600 parts of hot water and thehydrolyzed titanium values were recovered as a hydrate by settling,filtering and thorough washing. A recovery of 95% was obtained. Itshould be pointed out that the settling rate of the hydrate was 15cm./hr., the deliquoring rate was seconds and the washing rate was 135seconds. These rates are considerably better than the correspondingrates obtained in Example I which were 9 cm./hr., 220 seconds and 325seconds respectively.

The settling rate was determined by adding 200 parts of hydrate slurryto 300 parts of water and allowing the mixture to stand at roomtemperature. The supernatant liquid was measured in centimeters after 1hour.

The deliquoring rate was measured by pouring 100 ml. of the hydrateslurry at 50 C. into a 5.5 cm. Buchner funnel using two No. 55 Wh-atmanfilter papers at 18 inch Hg vacuum. The time in seconds to deliquor theslurry was recorded.

The washing rate was measured in seconds by passing 100 ml. of water at50 C. onto the deliquored filter cake under the same conditions.

The washed hydrate was bleached, washed, dewatered and calcined to atemperature of 925 C. in a rotary furnace. No dusting occurred in thecalciner during the calcining operation. The calcined product consistedof nodules to inch in diameter. These nodules were passed rapidlythrough a hammer mill (with no screen) to subdivide these nodules intogranules of a size such that they passed through a 20 mesh screen butwhich were retained on a 400 mesh screen with 90% +325 mesh. Thesegranules had a Tyler Screen analysis similar to that described inExample I.

The size of the individual particles in the granules were again similarto that described in Example I. The bulk density of the granularmaterial was 1.3 grams per cubic centimeter. The dust loss was 2.7% andthe material had a free flow of 6 seconds. Again no sludging nor dustingwas encountered when these granules were added to a glass batch.

From the above description and by the examples presented, it has clearlybeen shown that a new and novel type of titanium dioxide granularmaterial has been produced by the process of the instant invention. Thisgranular material is very different from titanium dioxide pigmentsproduced commercially. The granular material of the instant inventionmelts uniformly and rapidly in a molten glass bath without settling ordusting while regular pigment forms fiocs and settles to the bottom ofthe glass batch without melting.

The granular material of the instant invention is produced by a simpleand economical process which does not require the titanium solution tobe concentrated before hydrolysis. In addition the product does not haveto be severely milled, as is necessary in normal pigment productionprocesses, and further, the product is of such a character that eventhough it is severely milled, it will not not have pigmentaryproperties.

While this invention has been described and illustrated by the examplesshown, it is not intended to be strictly limited thereto, and othervariations and modifications may be employed within the scope of thefollowing claims.

We claim:

1. A process for the preparation of a nonpigmentary titanium dioxidegranular material, said granular material capable of being incorporatedinto a molten glass batch composition without dusting or settling insaid composition, said process comprising:

digesting a titaniferous material in concentrated sulfuric acid to forma digestion cake, dissolving said cake in aqueous media, reducing theiron values to the ferrous state, clarifying said solution to obtain atitanium sulfate-ferrous sulfate solution having a titaniumconcentration within the range of 100 to 180 g.p.l. titanium, calculatedas TiO and an H SO /TiO ratio of 1.7 to 2.3, adding said titaniumsolution heated to 40-80 C. to water heated to at least 80 C. withagitation over a period of -50 .8 minutes, the volume of water employedbeing from 10% to 100% of the amount of solution used, holding thetemperature of the mixture between 6080 C. during the addition period,heating the mixture over a period of from 15 to minutes until themixture reaches boiling temperature, then boiling said mixture for about1-3 hours to complete the hydrolysis of the titanium values and form aninsoluble titanium hydrate, filtering, washing and bleaching saidtitanium hydrate, and calcining the bleached titanium hydrate at800-1000 C. to form nodules of aggregated titanium dioxide particles,subdividing said nodules to form granules of TiO of a size to passthrough a 10 mesh screen but be retained on a 400 mesh screen, saidgranules comprising aggregated TiO particles having individual particlesizes which fall within the range of 0.05 to 0.15 micron.

2. Method according to claim 1 in which the size of the nodules formedare from /2 to of an inch in diameter.

3. A process for the preparation of a non-pigmentary titanium dioxidegranular material, said granular material capable of being incorporatedinto a molten glass batch composition without dusting or settling insaid composition, said process comprising: digesting a titaniferousmaterial in concentrated sulfuric acid to form a digestion cake,dissolving said cake in aqueous media, reducing the iron values to theferrous state, clarifying said solution to obtain a titaniumsulfate-ferrous sulfate solution having a titanium concentration Withinthe range of 100 to 180 g.p.l. titanium, calculated as TiO and an H SO/TiO ratio of 1.7 to 2.3, adding from 75% to of said titanium solutionheated to 4080 C. to water heated to at least 80 C. with agitation overa period of 1550 minutes, the volume of Water employed being from 10% toof the total amount of solution to be employed, holding the temperatureof the mixture between 6080 C. during the addition period, heating themixture over a period of from 15 to 75 minutes until the mixture reachestemperature, then boiling said mixture for about 10 to minutes, addingthe remaining 10% to 25% of the titanium solution to the hydrolysismixture and boiling the whole for 1-3 hours to complete the hydrolysisof the titanium values and form an insoluble titanium hydrate,filtering, Washing and bleaching said titanium hydrate, and calciningthe bleached titanium hydrate at 800-1000 C. to form nodules ofaggregated titanium dioxide particles, subdividing said nodules to formgranules of Ti0 of a size to pass through a 10 mesh screen but beretained on a 400 mesh screen, said granules comprising aggregated TiOparticles having individual particle sizes which fall Within the rangeof 0.05 to 0.15 micron.

References Cited UNITED STATES PATENTS 1,937,037 11/1933 Hanahan 23--2022,089,180 8/1937 Bousquet et al 23202 2,293,861 8/1942 Stark 106-3002,564,365 8/1951 Kingsbury 23202 XR 2,721,787 10/ 1955 Hettrick 232022,999,011 9/1961 Olmsted et a1. 23202 3,062,673 11/1962 Wigginton 23202XR 3,071,439 1/ 1963 Solomka 23202 3,091,515 5/1963 Dantro et al. 232023,211,528 10/1965 Wigginton 23202 OSCAR R. VERTIZ, Primary Examiner.

E. STERN, Assistant Examiner.

